1. Letters following this symbol are a WSSA-approved computer code from Important Weeds of the World, 3rd ed., 1983. Available from WSSA, 309 West Clark St., Champaign, IL 61820.
2. Some effects of the nitrogen supply on growth and development of Cirsium arvense
3. The control of bud dormancy in seed plants;Wareing;Symp. Soc. Exp. Biol.,1969
4. Organic food reserves in relation to eradication of Canada thistles;Welton;Ohio Agric. Exp. Stn. Bull.,1929